Value of Vasodilator Stress Myocardial Contrast Echocardiography and Magnetic Resonance Imaging for the Differential Diagnosis of Ischemic versus Nonischemic Cardiomyopathy

Objective Noninvasive differentiation of ischemic versus nonischemic cardiomyopathy (CM) remains challenging because of the low specificity of imaging-based tests in these patients. We hypothesized that myocardial contrast echocardiography (MCE) and cardiac magnetic resonance (CMR), combined with vasodilator stress, could provide accurate alternatives for determining the cause of CM. Methods To allow side-by-side comparisons between these techniques with coronary angiography as a reference, we studied 16 patients referred for coronary angiography after abnormal nuclear perfusion studies. Both MCE and CMR images were acquired within 48 hours with infusion of adenosine. MCE included flash-echo imaging during intravenous infusion of echocardiographic contrast solution. CMR included gadolinium injections for first-pass perfusion and delayed enhancement imaging. MCE and CMR images were reviewed by experienced investigators, blinded to the findings of the other modality and angiography. For each technique, each myocardial segment was classified as normal or abnormal. Sensitivity and specificity of each technique were calculated against the angiography reference. These calculations were also performed using a perfusion territory as a unit of analysis. Results Six of 16 patients had normal coronary arteries, and three patients had stenosis < 50%. By using this threshold for abnormal perfusion, segment-by-segment comparisons with angiography resulted in sensitivity of 0.88, 0.61, and 0.71 and specificity of 0.74, 0.86, and 0.94 for CMR perfusion, delayed enhancement scans, and MCE sequences, respectively. Using stenosis > 70% as a threshold resulted in a small decrease in both sensitivity and specificity (0.02-0.04) for all three techniques. Analysis of the ability of these techniques to detect an abnormality in at least one perfusion territory yielded sensitivity of 1.00, 1.00, and 0.86 and specificity of 0.78, 0.78, and 0.89, correspondingly, which were threshold-independent. Conclusions Both CMR and MCE perfusion imaging may be used to differentiate between ischemic and nonischemic CM. These emerging diagnostic tools may prove useful in strategizing treatment in these patients and thus avoiding unnecessary invasive procedures.